1. Field of the Invention
The invention relates to a composite diaphragm for diaphragm pumps that comprises an elastomer body and a coating of polytetrafluoroethylene (PTFE) on the product side. The elastomer body has the shape of a circular dish that has an edge with a clamping area, a bottom, and a flexible section of the diaphragm that connects the edge of the dish with the bottom.
The composite diaphragm is clamped in a diaphragm pump along the side of the edge, whereas the bottom of the composite diaphragm performs lifting movements. The flexible section of the diaphragm is turned inside out, with each lifting movement, whereby the roll-off movements of the flexible material are observed in a radial section. In the technical field, the flexible section of the diaphragm is therefore referred to also as a rolling loop.
2. The Prior Art
When using composite diaphragms where the flexible section of the diaphragm without a profile has a uniform wall thickness, white staining can occur in radial lines in the PTFE-coating that indicates the onset of material damage. As the damage to the PTFE-material progresses, the composite diaphragm loses its chemical resistance to aggressive conveyed media. The development of this damage limits the useful life of the diaphragm.
U.S. Pat. No. 5,349,896 discloses a design wherein the flexible section of the diaphragm is stiffened by radial ribs. The ribs extend from the transition area adjoining the bottom, up to the edge of the dish of the elastomer body. With a different number of radial stiffening ribs, it is possible to prevent the development of the damage described above. However, the roll-off property of the flexible section of the diaphragm deteriorates and the resistance to roll-off increases to a considerable extent.
When using this diaphragm with vacuum pumps, composite diaphragms are preferred that have a smooth surface on the product side and rest flatly against the surfaces of the pump when the latter is in operation. The invention provides a suitable composite diaphragm for diaphragm pumps that permits a long useful life without damage to the PTFE coating and uses good roll-off properties when the pump is in operation.